1. Field of the Invention
The invention pertains to a pressure medium-actuated unit including a cylinder with closed ends and an inside surface with a pair of diametrically opposed axially extending ribs, and a motor shaft with a pair of diametrically opposed axially extending vanes, wherein the vanes and the ribs bound first and second pairs of diametrically opposed working chambers between the motor shaft and the cylinder.
2. Description of the Related Art
Pressure medium-actuated units are generally used to support the operating movement of a component. The component can be subjected to an external load. In the case of a unit designed as a swivel motor, e.g., in the chassis of a vehicle, a stabilizer arrangement can execute a swiveling movement, but, during a spring deflection of the wheels of an axle, it is also subjected to a load of much higher frequency than the rolling movement of a vehicle body and thus to pressure changes in the supply of pressure medium.
This problem of the pulsation of the pressure medium is explained in DE 10 2004 051 444 A1, and as a solution, a foam body is proposed, which is placed in at least one working chamber of the unit. This foam body is associated at least with the disadvantage that the operating distance of the unit is limited. In addition, care must be taken to ensure that, over the service life of the unit, no decomposition phenomena occur which lead to the release of particles from the foam body, because these particles could cause clogging in the unit or in the pressure supply system.
DE 10 2004 039 767 A1, which represents the prior art, discloses a swivel motor including a cylinder with closed ends and an inside surface with a pair of diametrically opposed axially extending ribs, and a motor shaft with a pair of diametrically opposed axially extending vanes, wherein the vanes and the ribs bound first and second pairs of diametrically opposed working chambers between the motor shaft and the cylinder. First and second pressure medium ports are connected to respective first and second pairs of working chambers, each pair being connected by an interconnection system. The first working chambers alternate with the second working chambers, and at least one working chamber is connected to a pressure compensation element.
The pressure compensation element is formed by a pressure-limiting valve, which opens in the direction toward the working chamber with the lower working pressure, so that pressure medium can flow from at least one working chamber of a first group into a working chamber of the second group.
The pressure-limiting valve opens as a function of the pressure difference between two working chambers of different groups. The elastic deflection of a wheel can cause the load in a first working chamber to decrease, while the adjacent working chamber can be compressed. As soon as the pressure difference falls below a certain value, the pressure-limiting valve opens, even though the working pressure in the compressed working chamber has still not reached a critical value. With respect to its opening behavior, the pressure-limiting valve cannot distinguish between an allowable peak pressure in the compressed working chamber and a momentary pressure difference between two adjacent working chambers.
Another solution is proposed in DE 101 40 460 C1, according to which the pressure medium-actuated unit is connected to an external air cushion, which is intended to prevent cavitation in a working chamber.